Various embodiments are directed to systems and methods for modeling a multiplicative index, such as the BMA index. Many financial assets are valued based on indices that are multiplicative spreads over underlying indices. For example, many financial assets are valued based on the BMA Municipal Swap Index (the “BMA rate”). The BMA rate is an indicator of the market interest rate for tax-exempt municipal bonds issued by state and local governments. The BMA rate can be expressed as the appropriate London Interbank Offered Rate (the “LIBOR rate”) multiplied by a ratio, which is referred to as the BMA/LIBOR ratio.